The PIs' long-term objective is to develop and test the effectiveness of biomechanically-based rehabilitation strategies for improving upper extremity function and reducing pain and disability in persons with shoulder pathologies. Rotator cuff pathologies have up to 50% prevalence rates across several populations including persons with spinal cord injury, stroke, occupational exposure to repetitive overhead work, and athletes with repetitive overhead motion exposure. In the painful shoulder, there are two distinct impingement types, subacromial and internal (tendon undersurface contact). There is increasing evidence linking altered shoulder kinematics with disabling pain and dysfunction in these populations. The altered kinematics is hypothesized to reduce the space available for rotator cuff tendon clearance, resulting in impingement of the musculotendinous structures. However, there is very little direct evidence of rotator cuff clearance during arm motions. Past work has identified that without comprehensive 3D modeling and visualization, incorrect clinical interpretation can lead to misguided intervention strategies. The aims of this R03 application are to: 1) generate subject specific 3D shoulder anatomical models including rotator cuff muscle/tendon, coracoacromial ligament, and long head biceps soft tissue data; 2) identify the glenohumeral joint positions and motion alterations that most compromise or optimize rotator cuff tendon clearance across the physiological joint range of motion; and 3) validate that modeled positions identified in Aim 2 result in rotator cuff soft tissue impingement through in-vivo vertically open MR imaging and cadaveric pressure distribution testing. The PIs' approach for these aims will be to use high resolution MR imaging to reconstruct 20 subject specific comprehensive anatomical shoulder models. Using these reconstructions, modeling of position and motion alterations across the spectrum of physiologic range of motion will determine which specific kinematic positions and alterations most reduce, and which maximize rotator cuff tendon clearance with the coracoacromial arch or glenoid (Aim 2). Identified most and least risk positions will be validated cadaverically for pressure distribution, and in-vivo for direct visualization (Aim 3). The PIs' general hypotheses are that current clinical impingement test positions are not consistent with specific glenohumeral joint positions that minimize rotator cuff tendon clearance, and that potential positions and movements which optimize rotator cuff clearance are distinct for subacromial versus internal impingement. Comprehensive 3D modeling and visualization of shoulder kinematic effects on rotator cuff tendon proximity incorporating soft tissue data is a critical next step in understanding rotator cuff tendon mechanical impingement. This work is novel in its direct, comprehensive assessment of rotator cuff tendon clearance for all possible shoulder joint positions, and in its use of advanced subject specific modeling and imaging techniques. Subsequent investigations will further test exercise interventions derived from these data through randomized controlled clinical trials comparing to the current standard of care.